Known high pressure water mist systems, such as for example, HI-FOG® by MARIOFF CORPORATION rely on the production of water droplets, ranging between 50 μm-120 μm (microns), in which larger droplets entrain smaller droplets into the critical combustion region of a fire. Providing a desired mix of droplet sizes in the protected area using such as high pressure system requires careful location of the discharge points and a large quantity of water. The HI-FOG® system is a single fluid (water) system in which the fluid is delivered to the discharging nozzles at a high pressure for the 50 μm-120 μm droplet generation.
One type of device for use in such a system is described in WO 92/20453. Shown and described therein is a spray head with a number of nozzles arranged close to each other for a continuous directional fog spray.
Another water mist system and method is described in U.S. Patent Publication No. 20050000700. Therein is described a fire extinguishing method for high spaces such as engine rooms of ships in which a mist is provided in an unevenly distributed manner so that a circulating motion of the mist is created in the space.
Twin or dual fluid fire protection nozzles are shown and described in U.S. Pat. No. 5,312,041 and U.S. Pat. No. 5,520,331. In U.S. Pat. No. 5,312,041, shown and described is a dual fluid method and apparatus for extinguishing fires in which a nozzle discharges a first fluid in a path surrounded by a second fluid. In U.S. Pat. No. 5,520,331, shown and described is a convergent/divergent gas nozzle that atomizes a liquid provided through a liquid delivery tube having an aperture centered within a central gas conduit of an upstream mixing block connected to the nozzle.
Other water mist systems and nozzles are described in International Patent Application Publication Nos. WO 2003/030995; WO 2005/115555 and International Patent Application Publication No. WO 2006/132557 and U.S. Pat. No. 7,080,793. Other Mist generating devices are shown and described in International Patent Publication No. WO 2005/082545 and International Patent Publication No. WO 2005/082546, each of which is assigned to Pursuit Dynamics PLC, a named applicant in the instant application (outside of the U.S.).
WO 2001/76764 shows a mist generating apparatus which uses two fluids, primarily for use in fire suppression. In WO 2001/76764, a spray of first fluid droplets is created by forcing the first fluid through a number of aerosol nozzles in a conventional manner. The droplets are then carried by a stream of a second fluid through a convergent-divergent nozzle which sprays the combined stream of first fluid droplets and second fluid from the apparatus. The purpose of WO 2001/76764 is to reduce the pressure required to create the aerosol spray of the first fluid by using the second stream of fluid to carry the first fluid droplets out of the apparatus. The second stream also reduces frictional forces which can in some cases cause the first fluid droplets forming the aerosol spray to evaporate.
WO 2001/76764 does not use the second fluid in order to create the first fluid droplet regime. Instead, the droplets are created via an array of aerosol nozzles which create the droplets in a conventional manner. The stream of second fluid then carries the droplets through the spray nozzle without any atomization mechanism being applied to the first fluid by the second fluid. Thus, WO 2001/76764 still requires the first fluid to be supplied at relatively high pressure in order to create the aerosol droplets.